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signal (i.e., adding gain) and retransmits it after a programmed delay. Some setup parameters are written in a configuration file (e.g., hydrophone sensitivity, amplifier gain) and are not modifiable from the front panel. All other parameters are adaptable to the specific requirements. Once the configuration is set, the sys- tem can be started by pressing the start button on the system operation panel. The acquired signal is visualized in real time on a graph, together with all other related data, such as time, latitude, longitude and depth. The operator can decide to store or repeat the received signal or change con- figuration parameters to optimize perfor- mance.
TERAS was employed during the GLINT11 (Generic Littoral Interoperative Network Technology 2011) ASW experi- ment in the Gulf of Taranto in September 2011 and ExPOMA12 (Exercise Proud Manta 2012) multistatic ASW experiment in the Sicily Strait in February 2012, dem- onstrating reliable, calibrated target simu-
lation capability from both the CRV Leon- ardo and NRV Alliance. GLINT11 was fourth in an annual series of experiments demonstrating real-time offboard autono- mous AUV-based multistatic active sonar network technology. ExPOMA12 was the first opportunity to test the GLINT demon- strator as part of a NATO exercise.
The MERAS buoy's acoustic section during deployment. From the bottom up are the hydrophone and attitude sensor digitizer, twin projector and spherical hydrophone in its protec- tive cage.
Moored Echo Repeater To replace outdated technologies and try to better under- stand the effect of seabed and water-column parameters on the performance and effectiveness of an underwater system, NURC started modeling activities and at-sea campaigns in 2011 to quantify the differences between the models and the actual measurements, while including techniques to re- duce uncertainty in the input data.
The technology was to be moored on the bottom to limit signal fluctuations due to the echo repeater's motion. This new system also aimed to improve logistics and lower the cost of at-sea trials by elimi- nating a support ship for towing the echo repeater. The Moored Echo Repeater (MERAS),
now under final development and testing, comprises a moored surface buoy and a bottom-moored transducer assembly, which includes an Ultra Electronics Mari- time Systems Inc. (Dartmouth, Canada) MPS2-100 Projector, Neptune D/70 hy- drophone and Kulite ETM-375 pressure gauge connected together by electrome- chanical cable in a classical U-shaped mooring configuration. MERAS is particu- larly suited to situations wherein using a vessel is precluded by costs or weather conditions. The buoy hosts the control electronics and is lithium-battery powered. Battery re- placement does not require recovering the buoy. The buoy is connected via radio link (wireless local area network, ultrahigh frequency or FreeWave) to a remote com- puter for control, monitoring and configu- ration.
Energy consumption is minimized to
reduce the impact of the maintenance schedule on at-sea operations. This is achieved by the mix of components and
the ability to remotely switch subsystems on and off. The polymer lithium-ion battery was chosen for safety and en- ergy density, providing a total capacity exceeding 100 am- pere-hours at 24 volts DC. In this configuration, the echo repeater is able to drive an Ultra Electronics MPS2-100 pro- jector with a source level of 170 decibels, referred to 1 mi- cropascal at 1 meter. Overall autonomy is estimated at more than 33 hours, with a 10 percent duty cycle equivalent to roughly 12,000 pings of 1 second each.
34 st / NOVEMBER 2012
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